BEDFORD SHALE
The Bedford Shale of Ohio is
classically considered part of the Lower Mississippian, but age-significant
fossils in the Bedford Shale-Berea Sandstone-Sunbury Shale succession suggest
that the Devonian-Mississippian boundary should be questionably placed
somewhere in the Berea Sandstone interval. So, the Bedford is best
considered as near-uppermost Upper Devonian (upper Famennian Stage).
The Bedford is a
coarsening-upward succession, with grayish and reddish shales in its lower
parts and grading upward into interbedded shales, siltstones, and fine-grained
sandstones.
Early geologists placed
considerable paleoenvironmental and paleogeographic significance on the
differences between the “Gray Bedford” and the “Red Bedford” shales in the lower
parts of the formation. This has since been shown to be (in a simple
sense) a weathering artifact.
The lower Bedford Shale is
typically a grayish and reddish, soft clayshale succession, which weathers and
vegetates over quickly. Good exposures of the lower Bedford are uncommon
in Ohio.
Walnut Creek East Roadcut (Rt. 161 temporary
construction cut, northeastern Franklin County, central Ohio, USA)
Bedford Shale
Above & below are summer
2004 photos of a construction cut exposing very soft, grayish to reddish gray
to brick-reddish clayshales of the lower Bedford Shale. A good continuous
succession showing a basal gray shale unit, an overlying red shale unit,
followed by another gray shale unit was temporarily well exposed along the
northern & southern sides of Rt. 161 in the northeastern corner of Franklin
County, just east of the Rt. 161 and I-270 intersection & just east of
Walnut Creek Even these freshly exposed rocks do not stand up to water or
moisture very well (they practically fell apart when I washed up a few samples
under a faucet!).
Bedford Shale
Bedford Shale
The Bedford Shale is a very
sparsely fossiliferous unit, and fossils were not evident in this particular
outcrop or in the construction talus while in the field. However, one
specimen of the enigmatic alga Foerstia (aka Protosalvinia)
was noted in a piece of gray shale from this locality back in the lab. Foerstia
is abundant in a narrow interval of the underlying formation, the Ohio Shale.